Wiring board, method of manufacturing wiring board, and electronic device

ABSTRACT

A method of manufacturing a wiring board includes steps of: providing a substrate; forming a first wiring layer on the substrate by photolithography; forming a first insulating layer by ink jetting so as to cover a part of the first wiring layer and expose an exposed section of the first wiring layer; and forming a second wiring layer by ink jetting partly over the first wiring layer, with the first insulating layer being between the part of the first wiring layer and a part of the second wiring layer. A wider variety of conductive material and insulating material can be used for forming the wiring layers and the insulating layers on the substrate by ink jetting, while the wiring board has a first wiring layer having high density.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring board having a wiring layerformed in multiple layers, a method of manufacturing such wiring board,and an electronic device having such wiring board.

2. Background Information

Conventionally, wiring boards are manufactured by forming a wiring layerand an insulating layer simultaneously on the surface of a substrate.First, droplets of both a conductive material for forming the wiringlayer and an insulating material for forming the insulating layer aredeposited onto the surface of the substrate by ink jetting. Then, thewiring layer and the insulating layer are formed simultaneously on thesurface of the substrate as one layer. Thereafter, another layer of awiring layer and an insulating layer is formed by similar methods on topof the layer already formed. Thus, a wiring board having multiple layersof the wiring layer is obtained. The wiring layers are electricallyconductive relative to each other. Japanese Patent ApplicationPublication No. 11-163499 discloses an example of such wiring board.

In other words, the conventional technique entails forming the wiringlayer and the insulating layer simultaneously as one layer by inkjetting, and curing the layer by heating or the like. Consequently, itis difficult to use the two materials together when the heatingtemperatures at which the conductive material and the insulatingmaterial are deposited onto the surface of the substrate are different,or when the curing methods for the two materials, such as with heatingand ultraviolet ray irradiation, for example, are different. Also, thewiring layer and the insulating layer formed by ink jetting do not havea high density, unlike the high-density wiring boards formed byconventional additive methods or the like.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for improved wiring board,method of manufacturing wiring board, and electronic device having suchwiring board that overcome the problems of the conventional art. Thisinvention addresses this need in the art as well as other needs, whichwill become apparent to those skilled in the art from this disclosure.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a wiring board, amethod of manufacturing a wiring board, and an electronic device havingsuch wiring board, wherein a wider variety of conductive material andinsulating material can be used for forming the wiring layers and theinsulating layers on the substrate by ink jetting, while the wiringboard can have a first wiring layer having high density.

The wiring board according to the first aspect of the present inventionhas a substrate, a first wiring layer formed on the substrate byphotolithography, a first insulating layer formed by ink jetting so asto cover at least a part of the first wiring layer, and a second wiringlayer formed by ink jetting partly over the first wiring layer, with thefirst insulating layer being between the part of the first wiring layerand a part of the second wiring layer.

The method of manufacturing a wiring board according to another aspectof the present invention includes steps of: providing a substrate;forming a first wiring layer on the substrate by photolithography;forming a first insulating layer by ink jetting so as to cover a part ofthe first wiring layer and expose an exposed section of the first wiringlayer; and forming a second wiring layer by ink jetting partly over thefirst wiring layer, with the first insulating layer being between thepart of the first wiring layer and a part of the second wiring layer.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1(a)-(d) are schematic cross-sectional views illustrating the firsthalf of the method of manufacturing the wiring board according to thefirst embodiment of the present invention;

FIG. 2(3)-(g) are schematic cross-sectional views illustrating thesecond half of the method of manufacturing the wiring board according tothe first embodiment of the present invention;

FIG. 3(a)-(d) are schematic cross-sectional views illustrating themethod of manufacturing the wiring board according to the secondembodiment of the present invention;

FIG. 4 is a perspective view of a droplet depositing apparatus to beused to perform the manufacturing method of the present invention;

FIGS. 5(a) and (b) are plan views of a head unit and an ejection head ofthe droplet depositing apparatus shown in FIG. 4;

FIGS. 6(a) and (b) are a partial perspective view and a partial crosssectional view of a nozzle of the droplet depositing apparatus shown inFIG. 4;

FIG. 7 is a block view showing the configuration of the control unit ofthe droplet depositing apparatus shown in FIG. 4;

FIG. 8 is a schematic view of the manufacturing apparatus for the wiringboard to be used to perform the manufacturing method of the presentinvention;

FIG. 9 is a plan view of a liquid crystal display device including thewiring board of the present invention; and

FIG. 10 is an external view of a portable phone provided with a liquidcrystal display device having the wiring board of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The wiring board according to the first aspect of the present inventionhas a substrate, a first wiring layer formed on the substrate byphotolithography, a first insulating layer formed by ink jetting so asto cover at least a part of the first wiring layer, and a second wiringlayer formed by ink jetting partly over the first wiring layer, with thefirst insulating layer being between the part of the first wiring layerand a part of the second wiring layer.

In this wiring board, a second wiring layer formed by ink jetting isformed in an overlapped fashion over the first wiring layer that isformed by photolithography. A first insulating layer is provided betweenthe first and the second wiring layers. The insulating layer is providedonly where the second wiring layer is to be formed. Therefore, nomaterial is wasted and the amount of material used can be reduced. Also,since the first insulating layer and the second wiring layer are formedby ink jetting in an overlapped fashion over the high-density firstwiring layer formed by photolithography, a wiring board is obtained withbetter precision than when the insulating layers and the wiring layersare formed by the inkjet method alone.

In this case, the wiring board preferably further includes a secondinsulating layer formed by ink jetting so as to cover at least a part ofthe second wiring layer; and a third wiring layer formed by ink jettingpartly over the second wiring layer, with the second insulating layerbeing between the part of the second wiring layer and a part of thethird wiring layer.

According to this configuration, a second insulating layer and a thirdwiring layer are further formed in an overlapped fashion over the secondwiring layer, whereby a wiring board having a multiple wiring layers isobtained. By using the inkjet method, the wiring layer and theinsulating layer can easily be formed selectively in any necessarysections. Also, there is no need to perform a masking step, an unmaskingstep, and a plating step, nor is there need for any equipment to performthese steps. Thus, there are fewer manufacturing steps to be performed.Accordingly, the manufacturing costs can be reduced.

In this case, it is preferable that the first wiring layer has anexposed section that is not covered by the first insulating layer, thesecond wiring layer has an exposed section that is not covered by thesecond insulating layer, and the third wiring layer has an exposedsection that is not covered by the first or the second insulating layer.Furthermore, it is preferable that the second and the third wiringlayers are respectively connected to the exposed sections of the firstand the second wiring layers and made electrically conductive therewith.Still furthermore, an electronic component can be mounted on at leastone of the exposed sections of the first, second, and the third wiringlayers.

According to this configuration, the wiring layers formed into multiplelayers are electrically conductive with one another. Furthermore, thesubstrate can have various functions with an electronic componentmounted thereon, even when the substrate has a small planar surfacearea.

Furthermore, in the wiring board according to the present invention, theexposed section can be encircled by the first insulating layer. Stillfurthermore, the substrate can be a flexible substrate.

The method of manufacturing a wiring board according to another aspectof the present invention includes steps of: providing a substrate;forming a first wiring layer on the substrate by photolithography;forming a first insulating layer by ink jetting so as to cover a part ofthe first wiring layer and expose an exposed section of the first wiringlayer; and forming a second wiring layer by ink jetting partly over thefirst wiring layer, with the first insulating layer being between thepart of the first wiring layer and a part of the second wiring layer.

According to this method for manufacturing a wiring board, a secondwiring layer is formed in an overlapped fashion over the first wiringlayer. A first insulating layer is provided between the first and secondwiring layers. The first insulating layer is provided only to thesections where the second wiring layer is to be formed. Therefore,relatively less material is wasted, and the amount of material to beused can be reduced. Also, since the first insulating layer and thesecond wiring layer are formed by ink jetting in an overlapped fashionon the high-density first wiring layer that is formed byphotolithography, a wiring board having a better precision than onewhose insulating layers and wiring layers are formed with the inkjetmethod alone.

In this case, it is preferable that the manufacturing method furtherincludes steps of: forming a second insulating layer by ink jetting soas to cover at least a part of the second wiring layer and expose anexposed section of the second wiring layer; and a third wiring layerformed by ink jetting partly over the second wiring layer, with thesecond insulating layer being between the part of the second wiringlayer and a part of the third wiring layer.

According to this configuration, a second insulating layer and a thirdwiring layer are further formed in an overlapped fashion over the secondwiring layer, whereby a wiring board having multiple wiring layers isobtained. Using the inkjet method, the wiring layer and the insulatinglayer can be easily formed selectively in any necessary sections. Also,there is no need to perform a masking step, an unmasking step, and aplating step, nor is there need for any equipment to perform thesesteps. Thus, there are fewer manufacturing steps to be performed.Accordingly, the manufacturing costs can be reduced.

In the step of forming the first insulating layer of the manufacturingmethod of the present invention, the exposed section is formed bydepositing an insulating material so as to avoid the exposed section,encircling the exposed section with the first insulating layer.

In this case, the exposed sections are avoided and the first insulatinglayer is formed so that the exposed sections of the first wiring layerare not covered by the first insulating layer. The exposed sections areformed in the area in which the first insulating layer forms aconcavity. Using the ink jetting method, the first insulating layer canbe easily formed avoiding the exposed sections.

In the method for manufacturing a wiring board of the present invention,the step of forming the first insulating layer includes steps of forminga first-tier insulating layer by ink jetting so that an upper surface ofthe first-tier insulating layer is on the same level with an uppersurface of the first wiring layer, and forming a second-tier insulatinglayer by ink jetting so as to cover at least a part of the first wiringlayer and the first-tier insulating layer, so that the second-tierinsulating layer is between the second wiring layer and the first wiringlayer or the first-tier insulating layer.

According to this method of manufacturing a wiring board, the secondwiring layer is formed in an overlapped fashion over the first wiringlayer. The first insulating layer is provided across the first andsecond wiring layers. This first insulating layer is formed divided intwo layers. The first-tier insulating layer is formed up to the uppersurface of the first wiring layer. Therefore, the portion of the firstwiring layer that lies on the same plane as the first-tier insulatinglayer is not covered by the first-tier insulating layer, and thereforeis exposed. Next, a second-tier insulating layer is formed so as tocover the first wiring layer and the first-tier insulating layer betweenthe exposed sections connected by forming the second wiring layer. Thesecond-tier insulating layer can be formed more easily than when thesecond layer is formed so as to encircle the periphery of the exposedsections. Also, relatively little material is wasted and the amount ofmaterial to be used can be reduced. Furthermore, since the first-tierand the second-tier insulating layers and the second wiring layer areformed by ink jetting in an overlapped fashion on the high-density firstwiring layer that is formed by photolithography, a wiring board having abetter precision can be obtained than when the insulating layers and thewiring layers of the wiring board are formed only by ink jetting.

In this case, it is preferable that the manufacturing method furtherincludes steps of: forming a second insulating layer by ink jetting soas to cover at least a part of the second wiring layer and expose anexposed section of the second wiring layer; and a third wiring layerformed by ink jetting partly over the second wiring layer, with thesecond insulating layer being between the part of the second wiringlayer and a part of the third wiring layer.

According to this configuration, a second insulating layer and a thirdwiring layer are further formed in an overlapped fashion over the secondwiring layer, whereby a wiring board having multiple wiring layers isobtained. Using the inkjet method, the wiring layer and the insulatinglayer can be easily formed selectively in any necessary sections. Also,there is no need to perform a masking step, an unmasking step, and aplating step, nor is there need for any equipment to perform thesesteps. Thus, there are fewer manufacturing steps to be performed.Accordingly, the manufacturing costs can be reduced.

In this case, it is preferable that in the step of forming the wiringlayer, the wiring layer formed in an overlapped fashion is connected tothe exposed sections and made electrically conductive therewith.Furthermore, a manufacturing method can include a step of mounting anelectronic component on at least one of the exposed sections of first,second, and the wiring layers.

According to this configuration, the wiring layer formed in multiplelayers is configured so as to be electrically conductive. Furthermore,the substrate can have various functions with an electronic componentmounted thereon, even when the substrate has a small planar surfacearea.

In the step of forming the second-tier insulating layer, the second-tierinsulating layer can be formed only on sides of the exposed sectionalong which the second wiring layer extends across the first-tierinsulating layer and the first wiring layer.

In this arrangement, the second-tier insulating layer is provided to theexposed sections only on the sides on which the second wiring layerextends. The second-tier insulating layer can be formed more easily thanwhen the second layer is formed so as to encircle the periphery of theexposed sections. Also, relatively little material is wasted and theamount of material to be used can be reduced. Furthermore, since thefirst-tier and the second-tier insulating layers and the second wiringlayer are formed by ink jetting in an overlapped fashion on thehigh-density first wiring layer that is formed by photolithography, awiring board having a better precision can be obtained than when theinsulating layers and the wiring layers of the wiring board are formedonly by ink jetting.

The electro-optical device of the present invention is provided with thewiring board manufactured according to the method of manufacturing awiring board discussed above.

The electronic device of the present invention is provided with theelectro-optical device.

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

The wiring board, the method for manufacturing the wiring board, theelectro-optical device having the wiring board, and the electronicdevice of the present invention are described below with reference tothe accompanying diagrams. The wiring board discussed herein forms apattern on the surface of a substrate with conductive material, whilethis pattern is used as a wiring layer to carry out the function ofconnecting electronic components or the like. In this case, a pluralityof wiring layers are formed in an overlapped fashion on the substratesurface, and are electrically conductive with each other.

First Embodiment

FIGS. 1 and 2 are cross-sectional views showing the sequence of themethod of manufacturing a wiring board having wiring layers 2. FIG. 1shows the method of forming a wiring layer 2A (first wiring layer) and awiring layer 2B (second wiring layer), and FIG. 2 shows the method offorming still another wiring layer 2C over the wiring layer 2B. Thewiring layer 2A is a high-density wiring layer formed by conventionaladditive method. The wiring layer 2B and subsequently formed layers areformed by ink jetting in an overlapping fashion partially over thewiring layer 2A. The wiring layer 2A formed by the additive method canhave a precision whereby a pattern pitch can be as small as about 40 μm.

In contrast, the wiring layers 2B and the 2C are formed by an inkjetting method in which a pattern is formed by depositing conductivematerial as droplets. A far as the pitch patterns are concerned, aresolution of about 200 dpi and the pitch of about 120 μm are achievedwith the ink jetting method. The wiring board of the present inventionis obtained by efficiently combining a method of manufacturing ahigh-density wiring layer and a method for manufacturing a wiring layerby ink jetting.

The wiring layers 2 of the present invention is formed by first forminga wiring layer 2A, which is a conductive pattern, with the additivemethod on the surface of a flexible substrate 1, which is formed ofpolyimide, as shown in FIG. 1 (a). The wiring layer 2A is formed from Cu(copper), has a fine pattern, and is conductive. Next, an insulatinglayer 3A made of an epoxy resin is formed as shown in FIG. 1 (b) byphotolithography on the wiring layer 2A except where other electroniccomponents or wiring layers to be subsequently formed are to beconnected. Ni and Au are then applied by electroplating to the exposedsections of the wiring layer 2A not covered by the insulating layer 3A,thereby forming a plating layer 4. This plating increases the strengthof the wiring layer 2A, improves the conductivity with the other wiringlayer, and allows easier soldering.

The additive method of forming the high-density wiring layer 2A will nowbe described briefly. The additive method involves a first masking, inwhich portions of the surface of the flexible substrate 1 other thanpattern-forming portions are masked with a resist by photolithography.Next, Cu is applied by electroless plating to the pattern-formingportions which are not masked with the resist. The electroless platingis a method wherein the flexible substrate 1 masked with the resist isimmersed in a mixed aqueous solution of a Cu metal salt and a reducingagent, and the Cu is reduced and precipitated onto the patternedsection. When the resist is then peeled off, a pattern of the Cu isformed on the surface of the substrate 1. This pattern is the wiringlayer 2A. The electroless plating can be applied not only to Cu but alsoto other metals that are capable of forming metal salts. It is possibleto form the wiring layers 2A not only with the additive method but alsowith subtractive methods or other such methods.

Next, the wiring layer 2B is formed in an overlapped fashion over thehigh-density wiring layer 2A that is formed by the additive method.Before the wiring layer 2B is formed, an insulating layer 3B is formedso as to cover the wiring layer 2A leaving contact sections 2A′ (exposedsections) of the wiring layer 2A exposed, as shown in FIG. 1 (c). Thus,the insulating layer 3B is formed between part of the first wiring layer2A and the second wiring layer 2B. The contact sections 2A′ are to beconnected with the wiring layer 2B. The insulating layer 3B, as well asthe insulating layer 3A, is made of an epoxy resin. The insulating layer3B is formed, by depositing a liquid epoxy resin as droplets by inkjetting, partly where the wiring layer 2B will be later formed over thewiring layer 2A in an overlapped fashion. At this time, the insulatinglayer 3A and the insulating layer 3B may be formed simultaneously by inkjetting.

The method of forming the insulating layer 3B by ink jetting leaving thecontact sections 2A′ of the wiring layer 2A exposed will now bedescribed briefly. First, an insulating material is deposited onto bothends 7 of the contact sections 2A′ shown in FIG. 1(c) so as to exposethe contact sections 2A′. The insulting material is then furtherdeposited so as to avoid the contact sections 2A′, using the insulatingmaterial initially deposited on the ends 7 as a boundary. In thismanner, the insulating layer 3B is formed. In other words, the contactsections 2A′ are depressed concavities surrounded by the insulatinglayers 3B. The insulating layer 3B is cured by heat treatment afterbeing deposited by the ink jetting.

After the insulating layer 3B is formed, the wiring layer 2B thatconnects the two contact sections 2A′ of the wiring layer 2A is formedby ink jetting, as shown in FIG. 1 (d). The wiring layer 2B is formed bydepositing a conductive material in liquid form as droplets by inkjetting. After the wiring layer 2B is deposited, the depositedconductive material is baked by heating.

The conductive material is composed of a dispersion medium and Ag(silver) particles having an average particle diameter of about 10 nm.The Ag particles are dispersed stably in the dispersion medium. The typeof dispersion medium is not particularly limited to any particular typeas long as it is capable of dispersing Ag particles and does not causeaggregation. Known examples of such dispersion media include amines,alcohols, thiols, and the like. More specific examples include 2-methylaminoethanol, diethanolamine, diethylmethylamine, 2-dimethylaminoethanol, methyl diethanolamine, and other such amine compounds, as wellas alkylamines, ethylenediamine, alkyl alcohols, ethylene glycol,propylene glycol, alkyl thiols, and ethane dithiol.

These dispersion media are evaporated by heating, such that the wiringlayer 2B of Ag is left behind after the baking. The contact sections 2A′are subjected to Ni and Au plating, and the wiring layer 2B of Ag isdirectly connected to the wiring layer 2A, which is made of stillanother material Cu. In this manner, the connective strength andconductivity are improved.

Next, a wiring layer 2C that connects with the wiring layer 2B and thewiring layer 2A is formed in an overlapped fashion over the wiring layer2B. As shown in FIG. 2(e), an insulating layer 3C is formed, leavingcontact sections 2B′ (exposed sections), which are to be connected withthe wiring layer 2C and the contact sections 2A″ (exposed sections) ofthe wiring layer 2A, exposed on the wiring layer 2B. The insulatinglayer 3C, as well as the insulating layer 3B, is made of an epoxy resin.Also, the insulating layer 3C is formed by depositing a liquid epoxyresin by ink jetting, selectively only on portions that necessary toform the wiring layer 2C. After being deposited, the insulating layer 3Cis cured by heat treatment.

After the insulating layer 3C is formed, the wiring layer 2C thatconnects the two contact sections 2B′ and 2A″ is formed, as shown inFIG. 2(f). The wiring layer 2C is formed by depositing a conductivematerial in liquid form by ink jetting, and baking the depositedconductive material by heating, as in the case of the wiring layer 2B.The wiring layer 2B and the wiring layer 2C are both wiring layers ofAg, and do not need plating to improve conductivity. The wiring layer 2Band the wiring layer 2C formed by the ink jetting form dot shaped linearpatterns, which are characteristic of the ink jetting method.

Thus, the three wiring layers 2A, 2B, and 2C are formed on the surfaceof the substrate 1. It is possible to form a layered wiring thatincludes even more by repeating the steps shown in FIGS. 2(e) and 2(f).Also, electronic components 5 can be mounted on the wiring layers 2A and2C as shown in FIG. 2(g). A wiring board 6 provided with a layeredwiring 2 of multiple layers and electronic components 5 mounted thereonis thus obtained. The soldering capacity and the conductivity of theelectronic components 5 can be further improved if the wiring layer 2Cformed by ink jetting is coated with Ni and Au by a surface treatmentsuch as plating before the electronic components 5 are mounted.

The method of manufacturing the wiring board 6 having the three wiringlayers 2A, 2B, and 2C is described above. The effects of the method ofmanufacturing the wiring board will now be summarized.

(1) Since the layered wiring 2 can be formed by ink jetting multiplelayers in an overlapped fashion over the high-density wiring layer 2A,which is formed by the additive method, the layered wiring can havebetter precision than a layered wiring that is formed only by inkjetting.

(2) Where the wiring layers 2B and 2C and the insulating layers 3B and3C are formed by ink jetting, liquid materials can be deposited ontoonly necessary sections. Accordingly, little material is wasted.

(3) By forming the wiring layers 2B and 2C and the insulating layers 3Band 3C into multiple layers, it is possible to obtain a compact wiringboard 6. Particularly, it is possible to reduce the size of the wiringboard in the planar dimensions.

(4) The upper layers of the layered wiring 2 and the insulating layer 3are formed in separate ink jetting steps on the surface of the flexiblesubstrate 1, and are subjected to heat treatment at different times.herefore, the conductive material and the insulating material forforming the layered wiring 2 and the insulating layer 3 may havedifferent heating temperatures, for example. Accordingly, a greaterlatitude is afforded in the selection of the combination of materialsfor the layered wiring and the insulating layer.

(5) By forming the insulating layer 3 and the upper layers of thelayered wiring 2 by ink jetting, it is possible to form the layeredwiring 2 in multiple layers without using mask printing, peeling,electroless plating, and other such steps that require use of a resist.Therefore, the manufacturing process can be shortened.

Second Embodiment

Next, another method of forming the layered wiring 2 will be described.The difference between the methods of the first and the secondembodiments is in the use of the method of forming the insulating layer3B shown in FIG. 1(c). The insulating layer 3B of the first embodimentis depressed into a concavity such that the insulating layer 3Bencircles the contact sections 2A′ and exposes the contact sections 2A′.When the insulating material is deposited by ink jetting, the concavitymust be formed by controlling the depositing so that the insulatingmaterial is not applied to the contact sections 2A′. In this case, whennon-uniformities occur in the formation of the concavity, the concavitycollapses inward and the surface area of the contact sections 2A′ tendsto decrease. In this state, it is difficult to form the wiring layer 2Bfor connecting the contact sections 2A′. In the second embodiment, suchnon-uniformities are less likely to be caused during the ink jetting.

FIG. 3(a) shows a wiring layer 2A, an insulating layer 3A, and a platinglayer 4 formed by the additive method, as in the case described in FIG.1 (b). An insulating layer 3E (first-tier insulating layer) is firstformed by ink jetting in between the wiring layers 2A, as shown in FIG.3(b). In this case, the insulating material is filled from the flexiblesubstrate 1 up to the point where the upper surface of the insulatinglayer 3E is same level as the contact sections 2A′ in order to form theinsulating layer 3E. The wiring layer 2A acts as a dam for theinsulating layer 3E. Therefore, the insulating material should bedeposit in the prescribed amount necessary to fill in spaces between thewiring layers 2A. The insulating layer 3E does not cover the contactsections 2A′.

As shown in FIG. 3(c), an insulating layer 3F (second-tier insulatinglayer) is formed by ink jetting over the wiring layers 2A and theinsulating layers 3E where a wiring layer 2B that is to be connected tothe contact sections 2A′ is supposed to be formed with the insulatinglayer 3F between the wiring layer 2A or the insulating layer 3E and theinsulating layer 3F. In other words, the insulating layer 3F isdeposited so as to be in between the wiring layer 2B that will be formedlater and the wiring layers 2A and the insulating layers 3E that havebeen laid out already. The insulating layer 3F is formed only on thesides of the contact sections 2A′ along the direction in which thewiring layer 2B is supposed to extend across the insulating layer 3E andthe wiring layer 2A. Therefore, the insulating layer 3E does not formany concave insulating layer section encircling the contact sections2A′. The insulating layers 3E and 3F are cured by heat treatment afterbeing formed.

Next, the wiring layer 2B that connects with the contact sections 2A′ isformed by ink jetting as shown in FIG. 3(d). The wiring layer 2B isformed along the insulating layer 3F. Since the wiring material isdeposited along the edge of the insulating layer 3F, the wiring layer 2Bdoes not need to be formed any wider than necessary to define thecontact sections 2A′. The wiring layer 2B is baked by heating afterbeing deposited. The insulating layer 3 and the layered wiring 2 can besimilarly formed overlapping in multiple layers afterward.

The effects of the method according to the second embodiment explainedabove will now be described.

(1) The insulating layer 3F of the contact sections 2A′ is formed onlyon the side along which the wiring layer 2B is formed, instead of beingconfigured to encircle the concavity in which the contact sections 2A′is supposed to be formed. It is, accordingly, easier to control theformation of the insulating layer 3F by ink jetting.

Droplet Depositing Apparatus

Next, the droplet depositing apparatus for forming the layered wiring 2and the insulating layer 3 by ink jetting on the surface of the flexiblesubstrate 1 in the methods of the first and the second embodiments ofthe present invention will be described. The droplet depositingapparatus is an apparatus for depositing the liquid material asdroplets.

As shown in FIG. 4, a droplet depositing apparatus 10 has a headmechanism 12 having a head unit 20 for ejecting as droplets the liquidmaterial for forming the layered wiring 2 and insulating layer 3; a workmechanism 13 for mounting the flexible substrate 1 or another such workpiece (shown as work 30 in FIG. 4), which is the object onto which thedroplets are to be deposited from the head unit 20; a liquid materialsupply unit 14 for normally supplying liquid material for the dropletsto the head unit 20; a maintenance mechanism 15 for maintaining the headunit 20; and a control unit 16 for collectively controlling thesemechanisms and supply units.

The droplet depositing apparatus 10 has a plurality of supporting legs18 provided at the bottom, and a surface plate 19 disposed on top of thesupporting legs 18. The work mechanism 13 is disposed on top of thesurface plate 19 so as to extend in the longitudinal direction (X-axisdirection) of the surface plate 19. The head mechanism 12, which issupported by two supporting pillars 22 that are fixedly coupled to thesurface plate 19, is disposed partially on top of the work mechanism 13and extends in a direction orthogonal to the direction of the workmechanism 13 (Y-axis direction). The liquid material supply unit 14 forsupplying the liquid material to the head unit 20 of the head mechanism12 is disposed at one end of the surface plate 19. The maintenancemechanism 15 is disposed in the X-axis direction aligned with the workmechanism 13 near one of the supporting pillars 22 of the head mechanism12. Furthermore, the control unit 16 is housed underneath the surfaceplate 19.

The head mechanism 12 has the head unit 20 for ejecting the liquidmaterial, a head carriage 21 for suspending the head unit 20, a Y-axisguide 23 for guiding the movement of the head carriage 21 in the Y-axisdirection, and a Y-axis linear motor 24 disposed parallel to the Y-axisguide 23 on the side of the Y-axis guide 23.

The work mechanism 13 is positioned partially underneath the headmechanism 12 and is disposed along the X-axis direction with aconfiguration substantially similar to the head mechanism 12. The workmechanism 13 has a work 30, a work mounting stage 31 on which the work30 is mounted, an X-axis guide 33 for guiding the movement of the workmounting stage 31, and an X-axis linear motor 34 disposed parallel tothe X-axis guide 33 on the side of the X-axis guide 33.

In this configuration, the head unit 20 and the work 30 can move freelyback and forth in the Y-axis direction and the X-axis direction,respectively. First, the movement of the head unit 20 will be described.The head carriage 21 for suspending the head unit 20 is movably mountedon the Y-axis guide 23. Though not shown in the diagrams, there is aprotrusion that extends from the head carriage 21 to the side of theY-axis linear motor 24 that engages the Y-axis linear motor 24 to obtaina drive force, whereby the head carriage 21 can be moved along theY-axis guide 23 to any desired position. Similarly, the work 30 mountedon the work mounting stage 31 can be moved freely in the X-axisdirection.

Thus, the head unit 20 is configured to move to the ejecting position inthe Y-axis direction, stops there, synchronize with the X-axisdirectional movement of the work 30 underneath, and eject the droplets.A pattern or the like of the layered wiring 2 can be drawn on the work30 by controlling the movement of the work 30 in the X-axis directionrelative to the movement of the head unit 20 in the Y-axis direction.

The liquid material supply unit 14 for supplying the liquid material tothe head unit 20 has a liquid material tank 45, a liquid material pump44, and a flow duct tube 49 for connecting the liquid material tank 45to the head unit 20 via the liquid material pump 44. A plurality ofliquid material tanks 45 can also be provided instead of only one. Inthis case, each of the plurality of tanks is connected to the head unit20 through its own flow duct tube and liquid material pump. In thismanner, liquid materials with different functions can thereby besupplied to the head unit 20.

The head unit 20 holds six identically configured ejection heads 26, asshown in FIG. 5(a). FIG. 5(a) is a diagram of the head unit 20 asobserved from the side with the work mounting stage 31. Also, each ofthe ejection heads 26 for ejecting the liquid material has two nozzlerows 28, both extending in the longitudinal direction of the ejectionheads 26, as shown in FIG. 5(b). In this embodiment, one nozzle row has180 nozzles 27 are aligned in a row. When a plurality of differentliquid materials are used, the liquid materials to be ejected can beseparately assigned to the six ejection heads 26.

The ejection heads 26 each have a vibrating plate 63 and a nozzle plate64, as shown in FIGS. 6(a) and (b). A liquid collector 65 normallyfilled with the liquid material supplied from the liquid material tank45 via a hole 67 is located between the vibrating plate 63 and thenozzle plate 64. A plurality of barrier walls 61 are also locatedbetween the vibrating plate 63 and the nozzle plate 64. The sectionsenclosed by the vibrating plate 63, the nozzle plate 64, and a pair ofbarrier walls 61 constitute cavities 60. Since the cavities 60 areprovided so as to correspond to the nozzles 27, the number of cavities60 and the number of nozzles 27 are the same. The liquid material issupplied from the liquid collector 65 to the cavities 60 via supplyports 66 positioned between each pair of barrier walls 61.

A piezoelement 62 c and a pair of electrodes 62 a and 62 b on eitherside of the piezoelement 62 c are disposed so as to correspond to eachcavity 60 on the vibrating plate 63. A drive voltage is applied to thepair of electrodes 62 a and 62 b, whereby liquid material is formed intodroplets 68 and ejected from the corresponding nozzle 27. Anelectro-thermal converting element may be used instead of the vibratingelement 62 in order to eject the liquid material. Such configuration isdesigned to eject the liquid material by utilizing the thermal expansionof the liquid material through the activation of the electrothermalconverting element.

The maintenance mechanism 15 has the following maintenance units: acapping unit 56, a wiping unit 57, and a flushing unit 58, as shown inFIG. 4. The maintenance mechanism 15 further has a maintenance carriage51 for mounting the maintenance units, a maintenance carriage guide 52for guiding the movement of the maintenance carriage 51, a threaded part55 integrally formed with the maintenance carriage 51, a ball screw 54with which the threaded part 55 is threadably engaged, and a maintenancemotor 53 for rotating the ball screw 54. Thereby, when the maintenancemotor 53 is activated in the forward or backward direction, the ballscrew 54 rotates and the maintenance carriage 51 moves in thecorresponding direction along the X-axis direction via the threaded part55. When the maintenance carriage 51 moves to perform maintenance on thehead unit 20, the head unit 20 moves along the Y-axis guide 23 and stopsdirectly above the maintenance units.

The capping unit 56 of the maintenance units seals and caps all 12 ofthe ejection heads 26 in the head unit 20 when the droplet depositingapparatus 10 is not operating, thereby ensuring that the liquid materialdoes not dry to clog the nozzles 27 or cause other such problems. Thewiping unit 57 wipes off the liquid material and other matter adhered tothe nozzles 27 after continuous liquid material ejection or at the timecapping with a wiping cloth containing a cleaning solution, andmaintains all the nozzles 27 in a clean condition. The flushing unit 58receives the liquid material ejected from the nozzles 27 before thedroplet depositing apparatus 10 begins operating or the work 30 isprocessed, and confirms the ejection state of each of the nozzles 27.

The state of the ejection heads 26 can be maintained by thesemaintenance units to ensure satisfactory ejection conditions when thedroplet depositing apparatus 10 is not operating or during standby whenthe mounted work 30 is being replaced.

Next, the control unit 16 for controlling the configuration describedabove will be described with reference to FIG. 7. The control unit 16has an instruction unit 70 and a drive unit 80. The instruction unit 70includes a CPU 72, ROM 73, RAM 74, and an input/output interface 71,wherein the CPU 72 processes various signals inputted and outputted fromand to the input/output interface 71 based on data in the ROM 73 and RAM74, and outputs a control signal to the drive unit 80 via theinput/output interface 71.

The drive unit 80 includes a head driver 81, a motor driver 82, a pumpdriver 83, and a maintenance driver 85. The motor driver 82 controls theX-axis linear motor 34 and the Y-axis linear motor 24, and accordinglycontrols the movement of the work 30 and the head unit 20 with a controlsignal from the instruction unit 70. Furthermore, the motor driver 82controls the maintenance motor 53 to move the necessary units of themaintenance mechanism 15 to the maintenance positions. The head driver81 controls the ejection of liquid material from the ejection heads 26,such that a predetermined image is drawn on the work 30 by controllingin synchronization with the controlling of the motor driver 82. The pumpdriver 83 controls the liquid material pump 44 according to the ejectionstate of the liquid material, and optimally controls the supply ofliquid material to the ejection heads 26. The maintenance driver 85controls the capping unit 56, the wiping unit 57, and the flushing unit58 of the maintenance mechanism 15, and ensures that a satisfactorystate is constantly maintained in the nozzles 27 of the ejection heads26.

The instruction unit 70 is configured to send signals independently tothe plurality of vibrating elements 62 via the head driver 81.Therefore, the volume of the droplets 68 to be ejected from the nozzles27 can be controlled and varied for each nozzle 27 using the signalsthat are sent from the head driver 81 to each of the nozzles 27.

Manufacturing Apparatus

The manufacturing apparatus that can efficiently manufacture the wiringboard 6 will now be described. The manufacturing apparatus 100 of thewiring board 6 shown in FIG. 8 is a group of apparatuses that include adepositing apparatuses that deposits a conductive material for formingthe layered wiring 2 and an insulating material for forming theinsulating layer 3. The depositing device is the droplet depositingapparatus 10.

The manufacturing apparatus 100 has: a depositing device 103P forforming the insulating layer 3B, an oven 104P for heating and curing theinsulating layer 3B, a depositing device 103Q for forming the wiringlayer 2B, an oven 104Q for heating and baking the wiring layer 2B, adepositing device 103R for forming the insulating layer 3C, an oven 104Rfor heating and curing the insulating layer 3C, a depositing device 103Sfor forming the wiring layer 2C, and an oven 104S for heating and bakingthe wiring layer 2C, which are arranged in this order.

The manufacturing apparatus 100 unrolls a flexible substrate sheet 101that has been rolled up, and conveys the sheet to the feed port of themanufacturing apparatus 100. The flexible substrate sheet 101 is anexample of the rectangular flexible substrate 1. A high-density wiringsection 102, which corresponds to the wiring layer 2A, the insulatinglayer 3A, and the plating layer 4, is formed on the surface of theflexible substrate sheet 101. The manufacturing apparatus 100 forms aninsulating layer 3B with the depositing device 103P in an overlappedfashion on the conveyed wiring section 102. After the insulating layer3B is deposited, the manufacturing apparatus 100 conveys the wiringsection 102 to the oven 104P, where the insulating layer 3B is heatedand cured. Then, the manufacturing apparatus 100 conveys the wiringsection 102 to the depositing device 103Q to deposit the wiring layer2B, and after the wiring layer 2B is deposited, the wiring layer 2B isheated and baked in the oven 104Q. Similarly, the insulating layer 3C isdeposited and then heated and cured by the depositing device 103R andthe oven 104R, and the wiring layer 2C is deposited and then heated andbaked by the depositing device 103S and the oven 104S. In this manner, amultilayered wiring section 105 with a layered wiring 2 that hasmultiple layers such as is shown in FIG. 2(f) can be formed on thesurface of the flexible substrate sheet 101. Then, the flexiblesubstrate sheet 101 is cut and used as a flexible multilayered wiringboard 106.

Before the flexible substrate sheet 101 is cut out, the flexiblemultilayered wiring board 106 is obtained as a wiring board 6 bymounting the electronic components 5 as shown in FIG. 2(g). Themanufacturing apparatus 100 can also include an installation apparatusfor the electronic components 5 and a cutting apparatus for the flexiblesubstrate sheet 101.

Third Embodiment

Next, an embodiment of an electro-optical device having the wiring board6 of the present invention will be described. FIG. 9 is a plan view of aliquid crystal display device 200, which is an electro-optical devicehaving the wiring board 6. The liquid crystal display device 200 isincorporated into a portable phone or another such electronic device,and is used as a display section. The liquid crystal display device 200has a liquid crystal panel 201 for displaying various images, and awiring board 6 provided with a panel control unit for controlling theliquid crystal panel 201. The wiring board 6 has a flexible substrate 1,a terminal 202 for connecting the flexible substrate 1 with an externaldevice, a liquid crystal driver or another such electronic component 5constituting the panel control unit, and a layered wiring 2 forconnecting the electronic component 5 with the terminal 202.

The liquid crystal display device 200 displays the information inputtedfrom the terminal 202 on the liquid crystal panel 201 via the electroniccomponent 5. The multilayered layered wiring 2 is formed on the flexiblesubstrate 1 that is provided with the terminal 202 and the electroniccomponent 5. Therefore, the planar dimensions of the space needed toaccommodate the components can be reduced as compared with a wiringlayer configuration that is formed from a single layer. Also, a pliableflexible substrate 1 can be incorporated into portable phones and thelike with a configuration that extends along a curved surface, and canthus be used in a wide range of applications.

FIG. 10 is an external view of a portable phone, which is an example ofan electronic device provided with the liquid crystal display device 200shown in FIG. 9. The portable phone 300 shown herein has a main body301, and a display section 302 provided to be capable of opening andclosing. Operating buttons 303 are provided in alignment on the front ofthe main body 301. An antenna 304 is mounted to be extendable from oneend of the display section 302. A speaker is disposed inside thereceiver 305, and a microphone is mounted inside the transmitter 306.

The liquid crystal display device 200 is disposed on the display section302 along with the flexible substrate 1. Various images pertaining tophone communication can be displayed on the liquid crystal panel 201.The flexible substrate 1 provided with the electronic component 5functions as part of a portable control unit for controlling the entireportable phone. Also, the flexible substrate 1 having the multilayeredwiring layer makes it possible to reduce the size of the substrate, andallows the size of the portable phone 300 to be reduced.

The wiring board 6 of the present invention can also be applied to anelectro-optical device other than the liquid crystal display device 200,such as a plasma display device, an electroluminescence display device,an FED (Field Emission Display) with an electron emission element, anSED (Surface-Conduction Electron-Emitter Display), or the like.

Furthermore, aside from portable phones, the liquid crystal displaydevice 200 can also be mounted in various other electronic devices thathave display units. Specific examples include electronic dictionaries,portable game devices, calculators, wristwatches, small televisions,personal computers, navigations systems, POS terminals, and the like.

The present invention is not limited to the embodiments described above,and the following modifications are provided as additional examples.

(1) As the liquid conductive material, metallic particles other than Agparticles can also be used. For example, any one of the following, or analloy of any combination of two or more of the following may be used:gold, platinum, copper, palladium, rhodium, osmium, ruthenium, iridium,iron, tin, zinc, cobalt, nickel, chrome, titanium, tantalum, tungsten,and indium. However, Ag can be reduced at relatively low temperaturesand is therefore easily handled. Thus, as far as this aspect isconcerned, it is preferable to use a conductive material containing Agparticles when utilizing inkjet methods.

(2) The insulating material can be, other than epoxy resins, anymaterial that can maintain electrical insulation, such as one selectedfrom: polyimide resins, polyester resins, phenol resins, fluorineresins, ultraviolet curing resins, visible light curing resins, and thelike.

(3) Other than polyimide, the flexible substrate 1 can be made usingsynthetic resins such as an epoxy resin, a polyester resin, a phenolresin, or a fluorine resin as a base material; or can be a compositebase material made of a combination of these base materials.

(4) The flexible substrate 1 can be made of a nonflexible material,which may be glass or ceramic systems. The layered wiring 2 and theinsulating layer 3 can still be formed with the manufacturing apparatus100 even when the substrate 1 is nonflexible.

(5) Although the wiring layer 2A is made of Cu and the wiring layers 2Band 2C are made of silver in the above-mentioned embodiments, the samematerial may be used for the wiring layer 2A formed by an additivemethod and for the wiring layers 2B and 2C formed by ink jetting. Inthis case, the plating layer 4 is not needed.

The wiring board 6 of the present invention can be mounted in variousdisplay devices and also in various electronic devices other thandisplay devices, and can allow the size of the electronic device havingthe wiring board 6 and its manufacturing costs to be reduced.

The wiring board manufactured by the inkjet method has a wiring layerformed into multiple layers, and can be mounted in a liquid crystaldisplay device or another such electro-optical device. The manufacturingmethod allows the number of steps and the amount of material used by theinkjet method to be reduced, and is capable of resulting in a shorterdelivery date and reduced costs. Also, due to the multilayer structure,the wiring board can have reduced planar dimensions. Accordingly, theresulting liquid crystal display device or another such electro-opticaldevice can be mounted in a wide variety of electronic devices such asportable phones.

As used herein, the following directional terms “forward, rearward,above, downward, vertical, horizontal, below and transverse” as well asany other similar directional terms refer to those directions of adevice equipped with the present invention. Accordingly, these terms, asutilized to describe the present invention should be interpretedrelative to a device equipped with the present invention.

The term “configured” as used herein to describe a component, section orpart of a device includes hardware and/or software that is constructedand/or programmed to carry out the desired function.

Moreover, terms that are expressed as “means-plus function” in theclaims should include any structure that can be utilized to carry outthe function of that part of the present invention.

The terms of degree such as “substantially”, “about” and “approximately”as used herein mean a reasonable amount of deviation of the modifiedterm such that the end result is not significantly changed. For example,these terms can be construed as including a deviation of at least ±5% ofthe modified term if this deviation would not negate the meaning of theword it modifies.

This application claims priority to Japanese Patent Application No.2004-201882. The entire disclosure of Japanese Patent Application No.2004-201882 is hereby incorporated herein by reference.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents. Thus, the scope ofthe invention is not limited to the disclosed embodiments.

1. A wiring board comprising: a substrate; a first wiring layer formedon the substrate by photolithography; a first insulating layer formed byink jetting so as to cover at least a part of the first wiring layer;and a second wiring layer formed by ink jetting partly over the firstwiring layer, with the first insulating layer being between the part ofthe first wiring layer and a part of the second wiring layer.
 2. Thewiring board according to claim 1, further comprising a secondinsulating layer formed by ink jetting so as to cover at least a part ofthe second wiring layer; and a third wiring layer formed by ink jettingpartly over the second wiring layer, with the second insulating layerbeing between the part of the second wiring layer and a part of thethird wiring layer.
 3. The wiring board according to claim 2, whereinthe first wiring layer has an exposed section that is not covered by thefirst insulating layer, the second wiring layer has an exposed sectionthat is not covered by the second insulating layer, and the third wiringlayer has an exposed section that is not covered by the first or thesecond insulating layer.
 4. The wiring board according to claim 3,wherein the second and the third wiring layers are respectivelyconnected to the exposed sections of the first and the second wiringlayers and made electrically conductive therewith.
 5. The wiring boardaccording to claim 2, further comprising an electronic component mountedon at least one of the exposed sections of the first, second, and thethird wiring layers.
 6. The wiring board according to claim 3, whereinthe exposed section is encircled by the first insulating layer.
 7. Thewiring board according to claim 3, wherein the substrate is a flexiblesubstrate.
 8. An electro-optical device having the wiring boardaccording to claim
 1. 9. An electronic device having the electro-opticaldevice according to claim
 8. 10. A method of manufacturing a wiringboard, comprising the steps of: providing a substrate; forming a firstwiring layer on the substrate by photolithography; forming a firstinsulating layer by ink jetting so as to cover a part of the firstwiring layer and expose an exposed section of the first wiring layer;and forming a second wiring layer by ink jetting partly over the firstwiring layer, with the first insulating layer being between the part ofthe first wiring layer and a part of the second wiring layer.
 11. Themethod of manufacturing a wiring board according to claim 10, furthercomprising steps of: forming a second insulating layer by ink jetting soas to cover at least a part of the second wiring layer and expose anexposed section of the second wiring layer; and a third wiring layerformed by ink jetting partly over the second wiring layer, with thesecond insulating layer being between the part of the second wiringlayer and a part of the third wiring layer.
 12. The method ofmanufacturing a wiring board according to claim 10, wherein: in the stepof forming the first insulating layer, the exposed section is formed bydepositing an insulating material so as to avoid the exposed section,encircling the exposed section with the first insulating layer.
 13. Themethod of manufacturing a wiring board according to claim 10, whereinthe step of forming the first insulating layer includes steps of forminga first-tier insulating layer by ink jetting so that an upper surface ofthe first-tier insulating layer is on the same level with an uppersurface of the first wiring layer, and forming a second-tier insulatinglayer by ink jetting so as to cover at least a part of the first wiringlayer and the first-tier insulating layer, so that the second-tierinsulating layer is between the second wiring layer and the first wiringlayer or the first-tier insulating layer.
 14. The method ofmanufacturing a wiring board according to claim 13, further comprisingsteps of: forming a second insulating layer by ink jetting so as tocover at least a part of the second wiring layer and expose an exposedsection of the second wiring layer; and a third wiring layer formed byink jetting partly over the second wiring layer, with the secondinsulating layer being between the part of the second wiring layer and apart of the third wiring layer.
 15. The method of manufacturing a wiringboard according to claim 14, wherein in the step of forming the thirdwiring layer, the second and the third wiring layers are respectivelyconnected to the exposed sections of the first and the second wiringlayers and made electrically conductive therewith.
 16. The method ofmanufacturing a wiring board according to claim 14, further comprising astep of: mounting an electronic component on at least one of the exposedsections of the first, second, and the third wiring layers.
 17. Themethod of manufacturing a wiring board according to claim 13, wherein inthe step of forming the second-tier insulating layer, the second-tierinsulating layer is formed only on sides of the exposed section alongwhich the second wiring layer extends across the first-tier insulatinglayer and the first wiring layer.
 18. An electro-optical device,provided with a wiring board manufactured by the method formanufacturing a wiring board according to claim
 10. 19. An electronicdevice, provided with the electro-optical device according to claim 18.